1. Field of the Invention
The present invention relates to an ink cartridge that is a container for holding liquid to be supplied to an ink-jet recording head.
2. Description of the Related Art
An ink cartridge is a liquid container used for an ink-jet recording apparatus. In order to provide a good ink supply to a recording head that discharges ink, the ink cartridge is provided with a structure for controlling the power to hold ink in the cartridge. This power makes the pressure in an ink-discharging portion of the recording head lower than atmospheric pressure, and therefore is called “negative pressure.” A member generating this power is called a negative pressure generator.
Japanese Patent Laid-Open No. 06-328710 (corresponding to U.S. Pat. No. 6,231,172) proposes an ink cartridge including a liquid chamber that uses a negative pressure generator to absorb ink, increases ink capacity per unit volume of the ink cartridge, and is capable of stable ink supply.
FIG. 12A is a schematic sectional view showing an ink cartridge having such a structure. The interior of the ink cartridge 10 is divided into two spaces by a partition wall (bulkhead) 38 having a communicating hole (communicating portion) 40.
One space is a liquid chamber 36 that is hermetically sealed except for the communicating hole 40 and holds ink 25 directly. The other space is a negative pressure generator chamber 34 containing a negative pressure generator 32.
The negative pressure generator chamber 34 is provided with an air intake 12 through which air is introduced into the ink cartridge 10 with ink consumption, and an ink outlet 14 through which ink is supplied to a recording head (not shown).
In FIGS. 12A to 12C, the shaded area shows the ink held in the negative pressure generator 32.
As shown in FIGS. 12A to 12C, a groove 50 for facilitating air introduction into the liquid chamber 36 is provided in the vicinity of the communicating hole 40 between the negative pressure generator chamber 34 and the liquid chamber 36.
Ribs 42 are provided in the vicinity of the air intake 12 to form a space (a buffer chamber) 44 not containing the negative pressure generator 32.
In FIGS. 12A to 12C, the dashed line 61 at the top of the shaded area represents a gas-liquid interface. As ink is supplied to the recording head and consequently the ink in the negative pressure generator 32 is consumed, the gas-liquid interface lowers.
As ink is consumed, air is introduced from the air intake 12 into the negative pressure generator chamber 34. The air enters the liquid chamber 36 through the communicating hole 40 of the partition wall 38.
As air is introduced, the ink in the liquid chamber 36 enters the negative pressure generator chamber 34 through the communicating hole 40 of the partition wall 38, and the negative pressure generator 32 is filled with ink. This movement of air and ink is called “gas-liquid exchange.” As ink is consumed by the recording head for recording, the same amount of ink as consumed moves from the liquid chamber 36 to the negative pressure generator chamber 34 by gas-liquid exchange to fill the negative pressure generator 32.
By such gas-liquid exchange, the negative pressure generator 32 holds a constant amount of ink (maintains the level of the interface 61), and keeps the negative pressure in the recording head substantially constant. Therefore, ink supply to the recording head is stabilized.
Such an ink cartridge is productized by CANON KABUSHIKI KAISHA, and continues to be used.
Japanese Patent Laid-Open No. 08-020115 (corresponding to U.S. Pat. No. 6,137,512) proposes an ink cartridge using thermoplastic olefin resin fiber as a negative pressure generator.
This ink cartridge has excellent stability of ink storage. In addition, since the case and the negative pressure generator are formed of the same material, this ink cartridge has excellent recycling efficiency.
Recent ink-jet recording apparatuses have highly improved recording speeds and consume a large amount of ink for recording.
That is to say, the amount of ink to be supplied from the ink cartridge to the recording head per unit time is large.
In the above-described conventional ink cartridge, when a recording operation requiring a large amount of ink supply to the recording head is performed continuously, air supply from the negative pressure generator chamber 34 to the liquid chamber 36 becomes insufficient.
As a result, ink supply from the liquid chamber 36 to the negative pressure generator chamber 34 is interrupted, gas-liquid exchange becomes insufficient, and the liquid level (interface) in the negative pressure generator (liquid absorber) 32 lowers.
As a result, ink supply to the recording head becomes insufficient. Although some ink is left in the liquid chamber 36, the amount of ink in the negative pressure generator 32 decreases. Ink supply to the recording head can be interrupted. In such a case, recording cannot be continued.
How ink supply is interrupted in the conventional ink cartridge will be described with reference to FIGS. 12A to 12C. FIG. 12A shows gas-liquid exchange when a relatively small amount of ink is supplied from the conventional ink cartridge 10 to the ink-jet recording head (not shown).
In this state, the amount of ink supplied to the ink-jet recording head is relatively small. Therefore, the amount of ink going out of the liquid chamber 36 is the same as the amount of air introduced into the liquid chamber 36, in other words, the amounts balance out.
That is to say, the level of the gas-liquid interface 61 in the negative pressure generator 32 is kept substantially constant, in the vicinity of the point 51 where the upper end of the groove 50 comes into contact with the negative pressure generator 32.
In this state, the air passage when gas-liquid exchange is performed is the area around the point 51 in FIG. 12A. Three-dimensionally, the air passage is only part or all of the area around the line segment passing through the point 51 and extending perpendicular to the drawing, across the width of the groove 50. Therefore, if the amount of ink to be supplied to the ink-jet recording head significantly increases, it is impossible to introduce the same amount of air from the outside of the ink cartridge 10 via the negative pressure generator chamber 34 into the liquid chamber 36.
The same amount of ink as the amount of air that can be introduced from the negative pressure generator chamber 34 into the liquid chamber 36 through the above-described air passage moves from the liquid chamber 36 into the negative pressure generator chamber 34. In order to satisfy demand, a larger amount of ink than the amount of incoming ink goes out of the negative pressure generator 32 (operation A).
Therefore, as shown in FIG. 12B, the level of the gas-liquid interface 61 in the negative pressure generator 32 lowers.
Air goes out towards the liquid chamber 36 through the surface of the negative pressure generator 32 that faces the groove 50. Hereinafter, this surface 33 is referred to as the air outlet. With the lowering of the level of the gas-liquid interface 61, the area of the air outlet 33 increases and more air is introduced into the liquid chamber 36 (operation B).
By the combination of operations A and B, the level of the gas-liquid interface 61 lowers and the area of the air outlet 33 increases until the same amount of air as the amount of ink supplied to the head is introduced from the negative pressure generator chamber 34 into the liquid chamber 36.
Finally, when the amount of ink moving from the liquid chamber 36 into the negative pressure generator chamber 34 becomes the same as the amount of ink supplied to the head, the level of the gas-liquid interface 61 stops lowering, and it becomes possible to supply ink to the head without lowering the level of the gas-liquid interface 61.
However, at this time, lowering of the level of the gas-liquid interface 61 increases the negative pressure in the ink cartridge. This makes the ink supply to the recording head unstable, and affects the recording (printing) of the ink-jet recording apparatus.
In the case where the ink supply increases unexpectedly, for example, threefold or fivefold, the amount of ink moving from the liquid chamber 36 into the negative pressure generator chamber 34 cannot be the same as the amount of ink supplied to the head. The level of the gas-liquid interface 61 continues to lower at a faster rate than the increase in the area of the air outlet 33. Finally, as shown in FIG. 12C, the gas-liquid interface 61 reaches the ink supply port 14. This causes disruption of the ink supply to the head, and makes recording not possible.